Method of making matrices



Jan.

A. W. KLOMP METHOD OF MAKING MATRICES Filed June 1, 1956 2 Sheets-Sheet l v 1. Ii}. 5.

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INVENTOR. ALFRED W. KLOMP ATTORNEY.

Jan. 18, 1938.

A. W. KLOMP METHOD OF MAKING MATRICES Filed June 1, 1956 2 Sheets-Sheet 2 zos KLOM P BY mm ATTORNEY.

I Patented Jan. 18, 1938 I UNITED STATES PATENT OFFICE- mesne assignments,

to The Carbornndnm Company, Niagara Falls} N. Y., a corporation of Delaware Application June 1, 1936, Serial No. 82,871

5 Claims.

The present invention relates to metal casting and particularly to a method of casting matrices by means of which bonded abrasive gear wheels may be molded. v

' The use of a. bonded abrasive gear wheel as one of the mating gears on a machine for finishing or correcting the tooth contour of a metal gear has been recognized to present many desired advantages over the use of loose abrasive fed between conjugate metal gears. A bonded abrasive gear wheel, however, cannot be readily formed by means of well-known gear manufacturing methods. In other words, the teeth cannot be easily generated from an abrasive blank by any known gear cutting devices.

It is therefore an object of the present invention to provide a method whereby a metal matrix may be cast in such a manner that teeth forming recesses will be established therein which will impart proper tooth profile to an abrasive structure thatmay be molded in the matrix.

More specifically an object of the invention is to provide a metal casting that may be used as a matrix with gear teeth forming cavities which are free from pits, holes, cracks and like imperfections and at the same time provide the body of the matrix with sumcient mass and density to withstand the pressure incident to the molding of an abrasive gear therein.

Other and further features and objects of the invention will be more apparent to those skilled in the art upon a consideration of the accompanying drawings and the following description wherein an exemplary embodiment of the invention is disclosed.

In the drawings:

Figure l is a view in vertical axial section of a mold for casting a matrix in accordance withthe invention;

Figure 2 is a sectional view of one form of master gear showing means of removing the same from the casting;

Figure 3 is a plan view of the base of a master gear;

Figure 4 is a sectional view of one type of finished matrix showing a. bonded abrasive gear in section, as it may be molded in the matrix; I

Figure 5 is a sectional view of a pinion master gear;

Figure dis a view similar to Figure 4 showing a matrix in section formed from the pinion shown in Figure 5; and

Figures! and 8 are respectively sectional views of a beveled master gear, a matrix formed therefrom and a bonded abrasive gear after it has been molded in such a matrix.

The teeth of an abrasive gear for correcting the tooth profile of a metal gear and particularly teeth of generated form such as involute 5 I or cycloidal must be accurately shaped to properly abrade the teeth of the metal gear when two of such gears are meshed in conjugate fashion. A master gear of the desired type, size and tooth arrangement is therefore formed in the usual 10 manner as for example by generating the teeth from a metal gear blank with any of the wellknown gear cutting devices. The teeth of the master gear however, must be carefully shaped so that each tooth profile is perfectly formed 15 in regard to pitch and contour in order that the impressions formed in the matrix as hereinafter described will impart proper shape to the teeth of the bonded abrasive gear which may be molded in the matrix. 20 One type of such a master gear I0 is shown in Figure 1 positioned'with the large diameter ll downward and resting on the flat bottom portion H of a mold 13. This type of master is in the nature of a spur gear with the teeth 5 I 4 sloping towards the upper face 16 to provide this face with a smaller diameter and establish proper draft for removing the master from the matrix, formed in accordance with the hereinafter described method. The larger diameter 30 face H is provided with a plurality of elongated openings I! (Figure 3) which communicate with circular shaped recesses to receive the heads of T-shaped bolts I8. Suitable openings are provided in the bottom portion of the mold to per- 35 mit the threaded portion of the bolts iii to pass therethrough whereby the master may be held tight against the base of the mold by means of 0 nuts I 9.

The mold is supported in such a manner that 40 it may be rotated by means of a shaft 2| which is provided with an appropriate thrust bearing 22 for engagement with a support 23. Any wellknown mechanical device may be employed to drive the shaft 2| and rotate the mold such as a motor 24 suitably geared to the shaft 2! by 7 means of a gear 28 and a worm 21.

During the casting operation it has been found necessary to vibrate the mold and master carried therein to properly work the molten metal around the teeth of the master and remove any entrapped gases from the vicinity of the teeth. The mold may be vibrated during the pouring and cooling operation manually by striking the circular wall 28 with a relatively heavy hammer or mechanical means may be provided for such purpose such as a plurality of electromagnets 29 positioned around the periphery of the mold as indicated in Figure 1.

In .carrying out the casting operation arr-alloy consisting principally of zinc and specifically of 94% zinc; 5% aluminum and 1% copper, by weight, has been found to provide a suitable matrix possessing characteristics which make the formation tooth molding recesses possible. An alloy of such ingredients becomes molten at 900 F. However, more satisfactory results have been realized by heating the metal to approximately 1100" F. at which temperature it may be poured into the mold is from a suitable ladle 3i.

Pouring the molten alloy over the master which has been maintained at room temperature causes the alloy to be chilled so rapidly that cold-flows prevent a proper amount of metal-from moving into the vicinity of the teeth of the master and of course the tooth cavities of the matrix are not properly formed. The temperature of the master gear must therefore be raised to prevent premature congealing of the molten alloy. The temperature of the metal master, however, .must not be elevated to such an extent as to cause soldering of the alloy on the tooth surfaces of the master. Such a condition renders the removal of the master from the finished matrix impossible without marring the tooth forming corrugations. In order that soldering will not take place and cold-flows will be prevented, the master should be painted or otherwise coated with a mixture of sweet milk and graphite after which the master and particularly the toothed portion thereof is heated to 250 F. Heat may be applied to the master in any well-known manner such as by the use of a torch applied to the toothed portion after it has been positioned in the mold E3, or the entire master may be heated in a furnace prior to positioning in the mold.

With the alloy in a molten state at a temperature of approximately 1100 F. it may be poured in the mold and over the heated master. To prevent the air and gases that are trapped beneath the molten metal from forming pits, holes and the like in the casting, it is necessary that these gases be removed from the vicinity of the teeth and to replace the voids with molten metal. The mold is therefore rotated during the pouring operation at a relatively low speed to churn the molten alloy around the teeth of the master and thus work the metal into the gear teeth and force the air and gases upwardly through the spaces between the adjacent teeth of the master. Additional means of working the alloy into the corrugations of the master is provided by vibrating the mold during the pouring operation and thereafter as long as the metal is still molten. This vibration as above indicated may be accomplished by supplying an alternating current potential to the coils of electromagnets 29. The combined rotary and vibrating movements have a tendency to work the molten alloy around the teeth of the master and move any trapped gases from the vicinity of the teeth so that the teeth forming cavities of the finished matrix are free of pits and holes.

In addition to rotating and vibrating the mold it has also been found necessary to stir or puddie the molten metal at least in the vicinity of the teethof the master to properly work the alloy into all of the crevices of the master. The puddling operation tends to further remove the entrapped gases and should be maintained until the I compared to that of the ironmaster.

temperature of the molten alloy drops to approximately 925 F. or for such time as the casting metal remains molten.

After the alloy has congealed or hardened the matrix 30 formed thereby with the master embedded in one side thereof may be moved from the mold i 3 by removing the nuts ill to permit the bolts i8 to escape the opening in the bottom portion of the mold. The interior of the wall 28 is designed to flare slightly outward at the top to facilitate the removal of the matrix.

The matrix may then be turned in such a manner as to have the embedded master in on the up-. per side as shown in Figure 2. The master may then be removed from the matrix 3@ by securing the latter to a supporting base 32 with a number of clamps 33 and applying a power lift (not shown) to the eye hoolr 35 which in turn is secured to the master by means of the T-shaped bolts i8.

The removal of the master from the casting, however, should be accomplished while the temperature of the alloy is in the range between 600 and 700 degrees Fahrenheit. At these temperatures the zinc alloy acquires a sufiicient set to permit the matrix to be separated from the master and allows the tooth cavity portion to cool as soon as possible, thus avoiding distortion of these surfaces as a result of internal stresses set up by other portions of the matrix cooling first. An equally important reason for removing the master within the above indicated temperature limits is to avoid rupture of the casting as a result of the difierent coefficient of expansion of the alloy as In other words, if the more rapid shrinking alloy of the casting is permitted to cool below 600 F. before removing the master tension set up in the matrix around the addendum portions of the master teeth will cause the alloy to crack in the cavities of the matrix.

The matrix 3@ is shown in Figure 4 after the master ill has been removed. The teeth forming corrugations 35 are then of such shape that an abrasive mix may be pressed therein to form a bonded abrasive wheel 36 having teeth 37 which are of the same dimensions, contour and pitch as the teeth M of the master gear i0.

Various types of master gears having difierent tooth arrangements may be employed in connection with the above described method of casting a matrix. For example, a pinion master gear 10A as shown in Figure 5 may be fastened'in a mold similar to the mold l3 to form a matrix 30A as shown in Figure 6 and in which an abrasive pinion 36A may be molded. Such a type of abrasive gear is adapted to mesh with a beveled ring gear for abrading the teeth of the latter. illustrated is provided with straight teeth; however, spiral and helical toothed pinions may also be employed as the master as long aseach is provided with draft for removal from its respective matrix. In cases of spiral and helical gears the master must be free to rotate as the same is removed from its matrix. It is for this purpose that a swivel joint 38 is interposed in the lifting mechanism shown in Figure 2.

It may be desirable to abrade the teeth of a metal pinion and this maybe accomplished by means of a bonded abrasive ring gear 363 as shown in Figure 8. In this case the matrix 303 may be formed in accordance with the above described method by employing a master gear "B as shown in Figure 7.

A nickel cast iron consisting of 88% iron, 1.5%

The pinion' nickel and .5% molybdenum by weight has been foundto provide the various master gears with satisfactory characteristics in that good machineability is obtainable in generating gear teeth from a blankformed of such metal. The nickel a fiat base for the matrix for the purpose of permitting it to rest firmly on a support when the abrasive mix is later pressed therein to form an abrasive gear.

While specific mold apparatus and the preferred procedure have been described, it will be understood that the carrying out of the method is subject to variation in all respects within the bounds of the appended claims.

I claim:

1. The method of casting a matrix in which an abrasive gear may be molded, which comprises heating a metal master gear to a temperature of approximately 250 degrees Fahrenheit, pouring a molten alloy consisting principally of zinc into a mold and over the master gear while slowly rotating the mold at a speed sufllcient to work the molten alloy around the teeth of 'the master.

2. The method of casting a matrix in which an abrasive gear may be molded comprising the steps of heating an alloy consisting principally of zinc to approximately 1100 F. positioning a metal master gear in a metal mold, heating the master to approximately 250 F. and pouring the molten alloy into the mold over the master gear while the same is slowly rotated and vibrated to work the molten alloy around the teeth of the master.

3. The method of casting a matrix in which an abrasive gear may be molded which comprises positioning a metal master gear having sloping teeth in a cup-shaped mold, heating at least the toothed portion of the master to approximately 250 F., slowly rotating and vibrating the mold while a molten zinc alloy is poured into the mold over the master to work the molten metal around the teeth of the master, maintaining said movements until the molten metal has congealed, and thereafter removing the master from the casting.

4. The method of casting a matrix in which an abrasive gear may be molded which comprises pouring a molten alloy of zinc into a mold and over a metal master gear which has been coated with a mixture of sweet milk and graphite and heated to a temperature of approximately 250 F. to prevent adhesion of the alloy on the master, and to avoid chilling of the alloy, slowly rotating and vibrating the mold while the alloy is being poured and maintaining said movements of the mold until the molten metal has congealed.

5. The method of casting a matrix in which an abrasive gear may be molded which comprises pouring a molten alloy consisting principally of zinc into a cup-shaped mold and over a metal master gear which has been heated to a temperature that will prevent chilling of the molten alloy but which will avoid soldering of the alloy on the surfaces of the master, puddling the molten alloy in the vicinity of the teeth of the master gear before congealment of the alloy begins and thereafter removing the master from the casting when the temperature thereof cooled below 700 F. and before the temperature has reached 600 F.

. ALFRED W. KLOMP. 

